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How does a jet engine handle suddenly entering a lot of rain?
From my related question, it seems that an engine suddenly shut off would suffer from dangerous differential cooling from the airflow. This differential cooling would cause the engine to warp.
So now I'm wondering about a jet engine that suddenly enters rain. Wouldn't this initially cause severe differential cooling and thus warping, maybe even cracking? (P.S. would the same thing happen from entering a thick, dark cloud?)
How does the engine handle a huge amount of sudden rain ingestion? To me it seems like the sudden cooling on one side of the engine would cause thermal contraction, causing all sorts of problems.
EDIT: There seems to be a lot of comments about rain certification for engines and the fact that jets fly through rain all the time with no problem. I'm not questioning any of that. What I want to know is, how a jet engine handles the differential cooling caused by rain without warping or cracking?

I wish I could upvote a comment. Awesome one Tyler.

@GregTaylor You can. Hover your mouse just to the left of it.

Engines are tested extensively for ice and water ingestion, that video shows water being ingested at 4.5 tons per minute.

@RonBeyer Yes, what I was talking about was the sudden change in going from dry to super wet, not a steady state of wet. Specifically, the sudden differential cooling that comes from a sudden change. How does the engine handle that?

Pretty sure the tests involve getting the engine up to steady state then turning on the water/ice ingestion, otherwise it's not much of a real world scenario.

Injesting a large amount of rain can cause engines to fail.  For instance, the crash of a Southern Airways DC-9 in 1977: http://www.accuweather.com/en/weather-news/southern-airways-242-1977-crash/61989

@jamesqf It should be noted though that the hail was so bad it cracked the windshield, and a majority of the engine failure can be attributed to hail. While its speculation, I'm under the belief that if that flight did not encounter hail, the engines would have continued to run. Rain was a contributing factor at that point, but not the main cause.

@jamesqf ... and engines flaming out when ingesting rain doesn't happen anymore because the industry does what it's always done - makes the testing and certification better so that something can't happen again.  Modern engines are tested during certification with more water than any rain storm could introduce.  Watch the videos of this linked above and others.

If I remember right in what isn't mentioned in that article on the Southern Airways crash is that the hail clogged up the vent where excess water exited the engine.

When Qantas flight 32 had an engine failure on an A380 it severed controls to the left outboard engine. After landing the pilots were unable to shut it down so firefighters poured hoses into the intake until it flamed out. According to the Wikipedia article it took them 3 hours to get it to stop

@Simon: How much is due to being able to handle large amounts of rain (or rain in its solid form), and how much from having learned about false weather radar indications from that accident, so you don't fly through such weather in the first place?

The failure of both engines in TACA 110 was ascribed mainly to rain ingestion, with minor hail damage https://en.wikipedia.org/wiki/TACA_Flight_110

I edited the OP to clarify that what I'm interested in is not the rain certification, but rather the differential thermal cooling initially caused by rain. How does an engine handle that without warping/cracking?

Can you compute how much kg of water are in a ton of compressed air in your scenario? Not many likely. Several tons of air are pushed in the engine each second.

@mins: Is the weight of the air really relevant?  Surely it's the proportion of water to air that matters.  And compressing the incoming atmosphere would seem to make things worse, since it reduces the volume of air but not water.

@jamesqf: Not an expert, but most water could be centrifuged by the fan and never enter the core. The compressor vaporizes the rest before it enters the burners. Evaporation cools air, mass ratio is meaningful. With heavier cooled air, the DEC should inject more fuel. More heat can be created, more mass more accelerated. There is more oxygen in vaporized water than in dry air, and anyway more in dry air than necessary for a lean combustion. If water mass is too important, a compressor stall may be possible, and the flame can extinguish too. From what I read, the likelihood is low.

@mins: Re "There is more oxygen in vaporized water than in dry air...", you might want to consult a basic chemistry book about that.  If you had nothing but water vapor going into the engine, it would flame out immediately.

What makes you think the answer (with just two votes and no reference) to the linked question is actually substantiated? The most voted thing there (besides the question itself) is a comment that basically contradicts cooling issues would be the main reason.

@jamesqf: "There is more oxygen in vaporized water than in dry air..., you might want to consult a basic chemistry book about that." Thanks for pointing out a possible confusion, however I think there is 88.81% of oxygen in water (in mass). For dry air, there is 23.2% of oxygen in dry air. What figures had you in mind?

In another question there is an excellent answer for how thermal expansion is handled in a jet engine.  It's an established fact that jet engines can handle fast temperature swings.  Have you watched how fast an ITT gauge goes up when starting an engine? My answer will focus on rain's effect on a jet engine.
The first thing to understand is that jet engines take a lot of air. That's why they can handle bizarrely heavy rainfall or even water on the runway splashing into the engine from the tires (this water jet has the fun name "rooster tails"). The Airbus 320, for example, goes through 27,000 liters of air every second during takeoff. 2 That means even during rigorous FAA certification testing the concentration of water ingested never gets higher than 20 g of water for every cubic meter of air.  See FAA Part 33.78 Appendix B
In order for you to understand why the water has little cooling effect I have to describe what happens when an engine takes in water, assuming you know the basic parts of a jet engine.  The air/water mixture enters the compressor, and the fan blades in this compressor are spinning rapidly enough to catch a lot of the water and like a centrifuge this water is spun towards the walls.  This helps prevent water from entering the combustion path on a bypass engine, but it does not prevent water from following the gas path, especially on an engine with no bypass around the gas path.
The engine must now adjust for the extra water in the air, and engines are very good at adjusting for these kinds of changes in conditions.  If there's more than one independent compressor rotor, for example, the rotor speeds will change to keep the air moving smoothly and ensure a correct pressure drop across the compressor, called "compressor rematching."  The engine will also increase the fuel to air ration to compensate for the water.  These two processes evaporate the extra water through thermodynamic heating, not through heat transfer.  In essence, the first stages of the engine are providing the extra energy to evaporate the water, so little differential cooling occurs, even if the amount of rain is rapid.
One thing to note here is that the engine actually runs hotter than normal instead of cooler than normal during these events, due to the reasons noted above as well as the extra thrust provided from the water injection.
All the parameter changes noted above reduce your margins for engine flame out and compressor stall.  In practice, an engine should flame-out or surge before water can cause a big enough thermal change to cause engine damage.  If you think about it, the amount of temperature change needed to cause a problematic warping of an engine should be a lot more than the amount required to cause the engine to quit running.
So we've established that jet engines are good at expanding and contracting due to thermal changes.  We've also established that relatively speaking we're actually not talking about a ton of water here, just a few grams per cubic meter of air, which would take a small percent of the engine power to evaporate (~1% by my calculations). Most of the extra water is evaporated not by cooling down engine parts, but by making the early stages of the engine work harder.  Finally, the reduced margins caused by water intake mean that you'll surge or flame-out before you get to warping engine parts.  These principles should apply regardless of whether the water ingestion begins in a matter of seconds or ramps up over several minutes.
In conclusion, in "Investigation of Engine Power Loss and Instability in Inclement Weather,"(pdf)  the FAA noted "Engines typically are not damaged during a heavy rain encounter. Usually the most severe situation is to experience multiple engine flameout or surge with a subsequent pilot initiated engine shutdown."  The report then went on to note that the two incidents where engine damage had occurred from rain were over-temperature events, not from differential cooling.  So your biggest worry when flying through even storm-of-the-century rainfall should not be whether your engine will warp from rain cooling things down.

Thank you, this is a detailed and well-sourced answer. If possible, though, can you add more on the sudden change from flying in dry air to flying in rain? This is where I suspect a sudden temperature change might happen. BTW I invite you to weigh in on my other question, since it apparently has to do with differential cooling as well: http://aviation.stackexchange.com/questions/21464/why-do-jet-engines-take-a-long-time-to-throttle-down?lq=1

Edited my answer to better cover sudden changes. My argument here is that little or no sudden cooling would occur because water does not cause significant cooling of the engine parts without causing a flameout.   Is there a part of the engine you think would be exposed to a significant  amount of heat differences (without causing flameout), or is this a hypothetical question?

A flameout is defined as a loss of engine power that is not caused by a mechanical failure. The three items needed to keep a jet engine operating are fuel, air, and a source of heat to make them burn. Loss of any one of these three can result in a flameout.
Basically if the temperature in the combustion chamber gets too low you get a flameout. But the engine's controller detects lowering temperatures (due to the rain or ice ingestion) very quickly and adds more fuel to compensate for it.
There are (old) aircraft which have used water injection to increase engine performance, usually for take-off or engine failures, where it is needed the most. The reason the thrust is increased is because more mass (the water) is accelerated, but also that the temperature of the hottest section of the engine decreases, sod you can then add even more fuel to get a higher thrust without cooking the engines. If you add water to an oil based fire, it just explodes - a similar kind of energy is in play here.
Even in a strong storm, however, the main consequence of water ingestion a jet engine experiences is a reduction in the efficiency of the combustion process. This efficiency is a function of the fuel-air ratio that is changed by the presence of water vapor. This effect is negligible under most conditions since the percentage of water present in the large volume of air entering an engine is still relatively small in most storms. The high temperature in the engine's combustion chamber quickly evaporates this level of water into steam that has little influence on the engine's power output.


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Why was "taxi into position and hold" changed to "line up and wait" in the USA?
How come taxi into position and hold changed into "Line up and wait?" Did the old phraseology cause misunderstandings, or did it seem dated?

To ensure international consistency. Line up and wait is the standard phraseology used almost everywhere in the world, as defined by the ICAO, so it was confusing for pilots that another phrase was used to mean the same thing when flying to the USA.

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Why does a sport certificate have no distance restriction while recreational does?
A recreational pilot certificate only allows flights within 50 miles of home airport. A sport certificate has no distance limits even though it's easier to get - no medical certificate, less flying time and less instruction. What's the reason?

The recreational pilot certificate never really caught on.  As of October 2017 there are only 220 recreational pilots compared to 5,157 sport pilot certificates.  I think the reasons for this are reflected in your question.  Source:  https://en.wikipedia.org/wiki/Pilot_certification_in_the_United_States

Also supposedly the LSA category weight limit will be raised to 3,600 pounds but we will have to see if that actually happens.  The new limit would mean that most trainer aircraft like Piper Cherokees and Cessna 172s would be considered light sport aircraft and you could train for a sport certificate using these common rental aircraft.  Source:  https://www.avweb.com/avwebflash/news/LSA-Weight-Limit-Increasing-To-3600-Pounds-231639-1.html

The Recreational Pilot PTS and Sport Pilot PTS look nearly identical, but the key to your question can be found under AREAS OF OPERATION, Section I. PREFLIGHT PREPARATION.  Sport Pilots are required to demonstrate "Cross-Country Flight Planning", whereas Recreational Pilots are not.
Since they are not required to demonstrate the ability to plan a cross-country flight, unlike Sport or Private pilots, Recreational pilots are not allowed to perform them without an additional endorsement.

All of the answers and comments were helpful. Thanks all. This was the first that answered my original question so I gave it the checkmark. I knew when I asked the question that a rec cert could be endorsed for cross country. Can it get a blanket endorsement saying, in effect, that the rec pilot cert holder knows all the sport pilot stuff he was missing and should be able to fly anywhere, any time from now on, or is it limited to a specific destination one time only?

FAR 61.101(c)(3) does not specify any time, location or distance limits to the RPL cross-country endorsement, but the CFI could add some of their own, similar to a student cross-country solo endorsement. If you're going to do enough training for a CFI to consider a blanket endorsement, why not just upgrade to a PPL?

Because a sport pilot certificate requires the applicant to undergo at least three hours of cross country flight training whereas a recreational pilot certificate does not have that requirement.
I always got the impression that a recreational pilot certificate was essentially for people who had soloed and did not want to accomplish any other aviation goals save flying around their local airport.  Instruction is restricted to pre-solo aeronautical knowledge and skills.  It’s pretty limited in capability compared with a private pilot certificate, which explains why there are less than 600 recreational pilots registered by the FAA.
And one can expand a recreational pilot certificate to permit PIC on cross country flights over 50 nm, but this will require additional training and logbook endorsements by an instructor

Because the spirit of the regulations are a bit different and there is some history tied to this. The recreational pilot cert allows you to fly a lot of lighter common GA planes (J-3 Cub etc.) but limits you to one passenger and a local area. The idea being that the training is reduced a bit but you dont really need to worry about complex navigation, long range weather planning or any of the stuff that comes with flying a capable plane, far. The cert was intended mostly for local weekend fun in aircraft that were already easily rented.
The sport pilot cert was intended to birth a whole slew of aircraft but the type never really took off. Since new limitations were in place the hope was makers would build new planes but the reality was that a new sport plane cost well more than a nice used GA plane. You could often take the difference and get a full PPL as well as an instrument rating and still have some left over. Sport planes are fairly useable in some regards and pretty docile so the training was matched to the intended plane more than to complete with recreational.

A sport pilot can only fly LSAs, which excludes the C172 and most other 'typical' GA aircraft, if only because of the MTOW limitation of 1320lbs. There are rumors about the FAA increasing that limit to include more aircraft, but it hasn't happened yet.

Many aspiring pilots can't get a medical cert or use BasicMed, so SPL is their only option.  LSA rentals seem to be cheaper around here than non-LSA rentals, and you need fewer hours to boot, so the total cost of training should be significantly less than a PPL even for those without medical issues--if they can live with the limitations.

I think there is a typo in your second sentence. It refers to sport pilot certificates when you mean recreational pilot certificates. There are no limitations on distance for sport pilots but they are limited to aircraft with only two seats. Recreational pilots may fly in aircraft certificated for up to four passengers and are limited to local flights unless they get training and an endorsement for cross-country flights.

To put it short, the Recreational Pilot certificate allows you to fly common aircraft such as the Cessna 152. The Sport Pilot certificate was only created recently (2004), and it restricts the owner to Light Sports Aircraft - 1300 lbs MTOW or less.
Pilots on a budget normally get a well-used plane, and that's rarely an option for LSA, just because they're all quite new. Right now a well-used light aircraft can still be bought cheaper than a new LSA. So the Recreational path still has a lower financial entry barrier.
Long-term, the Sport cert appears to be meant to displace the Recreational. LSA restrictions are more practical and reasonable, given modern-day technology. Anyone who can't find a LSA that's good enough for them isn't likely to be satisfied with Recreational Pilot restrictions either, and will go for the proper PPL.

Thanks @Therac. My question was only about the distance limit. I was aiming for PPL long ago, then my life got complicated: marriage, children, etc. Now I'm ready to resume and I find that two new pilot certificate classes have been added. Sport pilot would be OK for me, at least for now, but the LSAs are big bucks to buy and there aren't all that many to rent. So I guess my question is more about the unfairness of it all.

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Are flexible pavements not recommended in hot climates?
I've received a feedback from an airport manager that flexible pavement is not recommended for runways within the regions of an extreme hot climates; this is because of the particles of asphalt that generate through the aircraft traffic along the time over runways, in which a potential risk on aircraft engines may occur by vacuuming these particles, and that some airports, accordingly, have replaced the runways' flexible pavement with rigid one. Is that true? Is there any new recent recommendations from ICAO or FAA in this regard??

I would think that the greater issue would be that black asphalt under a hot sun gets soft and the weight of aircraft traveling over it would cause ruts. This happens often on highways with cars and trucks, so I'd think it would be an issue at an airport, too. Especially when the aircraft is parked at a gate for a period of time. I'd imagine that different specs are used for the asphalt at airports than for roads, though, to mitigate the issue

You know, @mins, there was already an answer on this question that specifically mentioned flexible pavement in hot conditions. I was a bit out of it yesterday...

I can't speak to the current situation, but in the 1990s I often flew into Jeddah, Dhahran, and Riyadh, all in Saudi Arabia. It doesn't get much hotter in the summer than there, and all of the runways back then were asphalt. We did take care in the middle of summer in the middle of the day to slow to little more than walking speed when making a 90 degree turn as we found that the nose gear on a 747 would tend to slip occasionally in the extreme heat.

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Is it legal for an SEP airplane to fly above its service ceiling?
Let's take a Cessna 172R for example. According to the POH this airplane has a service ceiling of 13,500 ft.
I know that the service ceiling is the maximum altitude where a 100 foot per minute climb can be maintained.
So that would mean that it can technically continue the climb and fly well above his service ceiling, until full power is required for level flight (Correct me if i'm wrong here).
My question is, besides the physical barrier, is there any regulations that would prevent and aircraft to fly higher than his certified service ceiling?

the desire of the pilot to get back home is considered?

@Federico I'm asking about service ceiling, not max operating altitude, but I get your point! ^^

FlyingMag: 18,300 Feet in a Cessna 152: What I learned about flying

Provided you conformed to other flight rules, e.g. Airspace, supplemental oxygen, etc., there's no restriction against it.  But why would you want to?

You didn't say which country you're asking about, but in the US it's legal. Your definition of service ceiling is correct, and there's no regulation that I know of that requires you remain below it.
The only clear case I can think of would be if the POH says that the service ceiling is an actual limitation and you shouldn't operate above it. Exceeding limitations in the POH is a violation of 14 CFR 91.9(a):

Except as provided in paragraph (d) of this section, no person may
  operate a civil aircraft without complying with the operating
  limitations specified in the approved Airplane or Rotorcraft Flight
  Manual, markings, and placards

The AIM 5-3-3 requires you to report to ATC if you can't maintain a 500ft/min climb rate, so I suppose that not doing that could get you in trouble somehow. But there's no actual regulation, as far as I can see.
There are other, contrived scenarios that you could invent. If exceeding the service ceiling would require specific equipment or training that you don't have, then you could be in violation of various regulations, but that isn't because of the service ceiling itself.
And finally, there's the catch-all 91.13:

No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another.

If you do operate above the service ceiling and something goes wrong, then the FAA could bust you on that. Trying to get over mountains at or close to your service ceiling could be an example.

There's also the supplemental oxygen requirement.

@TomMcW Yes, that's the sort of thing I meant with my "equipment or training" comment. If exceeding your service ceiling means you need oxygen and you don't have it, you're violating 91.211. But you're violating a regulation on supplemental oxygen, not one on exceeding service ceilings.

It's important to remember that published service ceiling is based on a standard atmosphere. It's density altitude that is the reality of flying. On a 95 degF day in Albuquerque, the density altitude on the ground (elev. 5200 feet) is over 9000 ft.  Good luck getting even close to 10000 ft.  OTOH, on a cold winter day (0 degF) 13,500 ft density altitude may be above 15000 feet.

It is not illegal unless ceiling is listed as a limitation in the limitation section of the POH or AFM.  Simply mentioning a service ceiling does not make it a limitation, the service ceiling has to be a published limitation in the limitations section.
If your cruise performance tables only give numbers for 2700, 2500, and 2300 RPM can you run the engine at 2400 RPM?  Of course you can.  These values are not limitations, they're merely performance expectations (just like the ceiling figure).

As far as I know there is not FAR that requires you to abide by the POH numbers. However a case could most likely be made that this is careless or reckless operation,

§91.13   Careless or reckless operation.
(a) Aircraft operations for
  the purpose of air navigation. No person may operate an aircraft in a
  careless or reckless manner so as to endanger the life or property of
  another.

There are some other limits that could be imposed. First off FL180 and up is class A airspace and requires you to be going IFR. Subsequently you need to be equipped for IFR to do so, in turn you could not take a VFR only aircraft above FL180 in most scenarios.

Service ceiling may be exceeded in the US, not withstanding operational restrictions from the manufacturer and regulatory altitude restrictions such as O2 requirements, ATC, etc.
In general your chances of exceeding the service ceiling are greater with a light load, and in cooler temperatures, where your performance is better.  Flying in the middle of a low helps as well, because there is a light updraft. It is a somewhat common occurrence when flying in some mountainous regions (particularly in South America), where mountain wave will provide additional lift.  The conservative pilot may choose to take the altitude from the wave, figuring that when they are out of it, there will be a strong downdraft.
Flying unforecast mountain wave I have encountered -2000++ VSI readings flying at Vy in the downdraft region, and +2000++ VSI readings flying near Vmo or Vne in updrafts.
Bottom line to remember, your practical service ceiling is impacted by atmospheric conditions, and to a larger extent loading.


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Which fonts were used in old (1930s) aircraft cockpit displays and instruments?
This is probably more of a graphic design question than aviation but maybe a few hangar rats around here know the answer.
What type fonts were used on the old instruments in aircraft from the 1930s like Lockheed Vegas, Electras, Beech Staggerwings, DC-3s, etc.?  I need it for a web site I’m working on.

No doubt that'd depend heavily on the specific aircraft and instrument, different manufacturers will use different fonts.

Is "font" even a meaningful concept here?  I would guess that a draftsman (or woman) simply drew a master for the dial face.

I've seen a few times that even hand-written markings were used. This suggests that there hardly was any consistency.

Photo from Darwin Aviation Museum:

I'd suspect DIN 1451 in European aircraft of that era. This typeface was standardized originally in 1931, but has origins in 1905.
Notably, Airbus uses DIN 1451 in its labeling today, and Boeing uses Futura.

I'm not sure why you'd extrapolate DIN to be European - it's a German specification and the Germans weren't exactly on a hugely friendly footing through that period... I doubt many other European countries used it and definitely not Britain and France!

@Dan Because it's true. Look at this Fokker D.XXI cockpit, it looks like DIN 1451 on the airspeed and distance gauges. Why is the SU-95 in Airbus blue with DIN font? Same reason: common suppliers and de-facto standards.

I really don't buy it to be honest. Germans didn't have some kind of hold on Pre-War aviation that would mean their standards became defacto, Maybe Fokker did use some German gauges, but again, that doesn't extrapolate to 'European aircraft'.

@Dan There's clear evidence that DIN font was used on German and non-German aircraft of that era. The font shows up in a lot of technical applications. The font is still being used on European aircraft 80 years later. Like today, there's limited suppliers for instruments. It's the first place to look, maybe not for British aircraft (which seem to be more US-aligned), but for everybody else.

Is there clear evidence? I mean, you've found 2 gauges (out of however many) on a neighbours aircraft that may have done. It just feels a bit over-simplistic to me - Europe is a big place and I don't think it's right to presume that a random sample of gauges from that era would be centred around DIN 1451. I'm not sure it matters what's used today especially as Airbus wasn't founded until the 70's

For instrument faces, my bet would be Futura; a sans-serif typeface introduced in the 20s and one of the most widely used in graphic labels.  Possibly Univers, but that was introduced in the 50s.

Old Soviet aircraft had pretty standardised fonts, I believe. I shall try and find some to put up here. They were similar to COURIER NARROW but we'll have to see.

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Does a type rating give a person the privileges of an instrument rating in any category or class of aircraft which he/she is certificated in?
Suppose someone obtains a PPL-ASEL, then obtains a type rating in an aircraft requiring that rating e.g. jet, etc.  This type rating functions as an instrument rating, allowing the pilot to fly the new aircraft under IFR.  But does said type rating then grant the pilot the privelages to operate ANY appropriately equipped airplane single engine land under IFR as well?

Under which jurisdiction?

United States of America

I'm pretty sure you'd have to have an instrument rating first...

No I was informed about this by an FAA ATP examiner who also issues type ratings on the Lear 25,35, and 65 airplanes.  The type rating also functions as an instrument rating and is required to do so as the airplane's flight envelope extends into Class A airspace requiring IFR operations there.

To clarify, you are asking about a type rating added to a private certificate exclusively, not a type rating ride that doubles as an ATP check ride? The ATP Certificate does give instrument privelages.

61.63(d)(1) requires that if you don't have an ATP that you hold an instrument rating to obtain a type rating. The type rating itself does not grant instrument privileges.

(d) Additional aircraft type rating. Except as provided under paragraph (d)(6) of this section, a person who applies for an aircraft type rating or an aircraft type rating to be completed concurrently with an aircraft category or class rating—
(1) Must hold or concurrently obtain an appropriate instrument rating, except as provided in paragraph (e) of this section.

Paragraph (e) exempts aircraft incapable of instrument maneuvers and instrument flight from this requirement.
This does mean that you can do the instrument checkride concurrent with the type rating. If your hypothetical PP-ASEL gets typed in a citation, he will end up with a PP-ASEL with instrument airplane rating and the citation type.


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Is there a special kind of fuel needed to obtain high efficiency engines?
Are there any special kinds of fuels that manufacturers are considering in order to make high performance, high efficiency jet engines?

ساخت موتور جت کم مصرف با قدرت بالا . سوخت چه چیزی باشد
Construction of energy-efficient high-power jet engines. What is Fuel

I know I edited this a lot, but I'm fairly confident this is what the OP meant to say.  Just trying to help get it translated into English...  If someone who speaks Arabic could go ahead and translate his actual text in the above comment, that would probably be even better...

NOTE: that's no Arabic, that's Farsi (Persian) [I have some friend that speak it, I will see if they can help]

@Federico ......oops.  So, yeah, what I said above except, you know, Farsi.

@JayCarr from a friend of mine: "Apparently he wants to know what kind of fuel must be used in order to make a fuel-efficient high power jet engine" [basically what you guessed] "Or which jet engines are high power and at the same time consume less fuel and which fuel would help do that"

Surprisingly, it isn't a big factor in GA or commercial aviation.
                            Specific  Energy
                            Energy    Density
                            MJ/Kg     MJ/L
Diesel / Fuel oil           48        35.8
LPG (inc Propane / Butane)  46.4      26
Jet fuel (Kerosene)         46        37.4
Gasoline (petrol)           46.4      34.2
HMX (Rocket Fuel)            5.7      10.8

Even high-performance long-range military aircraft like the U2 and SR-71 use some variant of Kerosene with additives, their fuels are optimized for high flash point, not for energy density or for specific energy.
Generally, availability and infrastructure trump efficiency.

Wikipedia: Energy Density
Aircraft Diesel Engine

Has nobody designed a high efficiency engine off of liquid Hydrogen or Methane?  Both have a higher energy density than Jet Fuel it looks like, and liquid Hydrogen is becoming more and more available all the time...

@JayCarr You have to look not only at energy density but the safety aspect. There is a reason nobody is within miles of a rocket launch, when liquid hydrogen explodes, it explodes. JET-A is relatively stable, but even with that fuel there was a push a while ago to develop an anti-misting kerosene that was abandoned, but the goal was to develop a fuel that wouldn't atomize and burn in a crash.

@RonBeyer They use liquid hydrogen in cars these days, both in hydrogen fuel cells and in vehicles that burn the hydrogen directly.  I admit it's been troublesome in the past, but I don't know that those safety concerns matter anymore.  Further, I'm only asking if someone may have given it a shot, a lab will care for less about how safe it will be in a car when they are first developing the technology.

@JayCarr: The Tupolev 155 used three hydrogen-powered jet engines, and Wikipedia lists 10 more hydrogen-powered aircraft, most of which never came (or most likely never will come) to fruition. The Kusnezov NK-88 is my answer, but cryogenic storage pretty much nullifies the advantage of hydrogen's higher energy density.

@PeterKämpf I wonder if that technology will significantly change as more cars switch over to hydrogen...  I assume so, but I guess we'll see.


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How can an airliner make up for time lost?
If a plane has been delayed at the origin how does it make up for the lost time? Does the pilot need any special permission from ATC to increase the speed so that it can cover the lost time or has the pilot the power to make such kind of decisions?

Hello LearningPhase, welcome to Aviation StackExchange!

I feel like there was another question about an airplane making up for leaving late, but I can't find it now.  I did find this question which is related and could also be interesting for you.

A lot of times the pilot can't increase speed, so the only resolve is to have less time at the gate at the destination airport before turning around. I can't tell you how many flights I've been on that arrived late, and missed my connection. Or arrival flights that came in late and had short turn around times.

It's worth noting that flight schedules frequently have some extra time built in (e.g. a flight that's only in the air for 35 minutes commonly has 1:05-1:15 scheduled in my experience,) so even a flight that's delayed in departure by 20 minutes often arrives on time if it encounters no other delays.

Possible duplicate of Who decides how fast commercial aircraft fly: the pilots or ATC?

Thank you for all the answers. Cleared all my doubts about it. Had a conversation with my dad about it last night which have me the idea to put this question on the SO. Thanks again

Ludicrous Speed. (Sorry, couldn't resist).

According to ICAO Annex II (Rules of the air) 3.6.2.2(b):

Variation in true airspeed: if the average true airspeed at cruising
  level between reporting points varies or is expected to vary by plus
  or minus 5 per cent of the true airspeed, from that given in the
  flight plan, the appropriate air traffic services unit shall be so
  informed.

So the pilot in command has the right to increase speed, just as well as the air traffic controller has the right to limit it. However, as airliners normally cruise fairly close to their maximum speeds, this isn’t very effective. Recovering lost time by increasing speed is at best 1 to 3 minutes per hour.
Better ways are to request possible shortcuts from ATC and change altitude for better wind and temperature.

@LearningPhase, it's customary on StackExchange sites to wait a decent amount of time before accepting an answer to give other people a chance to provide what could be a better answer.  I personally wouldn't accept an answer for at least 24 hours, and then probably longer than that.  This might be the best answer, but you may never know if you accept too soon.

@KirkWoll, Oh, of course, but questions with an accepted answer are far less likely to get additional answers so a better answer may never come.

Also, fuel efficiency drops pretty rapidly when you push much past ideal cruise speed.  There is a certain reluctance to pick up time simply by running the engines harder as it can be rather expensive in fuel to do so.

As an example: I was flying to Phoenix from the east coast.  A combination of leaving slightly late and a headwind, resulted in an estimated time of arrival that was almost an hour late.  The pilot requested and received a change in flight path (lower altitude and a more southerly route, I believe) that resulted in arriving on time.  Actual distance covered was actually greater, but the lack of the heavy headwind more than made up for that.

@JPhi1618 down with the green checkmark tyrant! power to the upvotes!

@Sami Are those ICAO Annex II rules fully enforced in every  country (say 1st world country) airlines operate? And are they for commercial or IFR flights only, or general avaition / VFR too?

"the air traffic controller has the right to limit it" <-- Come again?

@Xen2050 That particular part is from flight plan filling, and it clearly states that the commander has the right to adjust his speed, but must inform ATC. I can't say about every country, but most have adopted Annex II as it is. Ofcourse the are airspace limitations etc, but I adressed the question in a more general view.

@MortensenAviation ATC can instruct an aircraft to increase, reduce or maintain a specific speed.

@Sami show us a reference that says it is mandatory for the pilot in command to accept it.  Yes, a controller may make the request, but the pilot can refuse it in a location without statutory speed limits.

@MortensenAviation Sigh.. Yes, I'm sure I as a pilot could refuse. I could also refuse going through a safety inspection at an airport. As a result, I would most likely stay out of the aircraft. Take it far enough, I'm sure I could also refuse eating, sleeping and breathing up to a certain point, after which it begins to make my life very complicated.

Also this http://aviation.stackexchange.com/a/7927/8321 has some regulation text on it.

@Sami it looks like you may be right.  Perhaps the "a pilot can turn down any new ATC instruction" is an urban myth perpetuated throughout the GA community by professors in their 50's.

@MortenseAviation Not entirely. A pilot can disregard any and all regulations when it is necessary for the safety of the flight.

That's a common scenario, that you're pushing off the gate late and would like to make up time.  There are a number of ways that making up time can happen, although how much of that the pilot can affect doesn't often amount to a huge impact.
The flight is scheduled for whatever length of time, gate-to-gate.  This accounts for the sorts of delays that the planners foresee when they're building the schedule: it's winter, so the aircraft may need to be de-iced.  It's a busy time of day, so they plan on a slower taxi than simply driving out to the runway & taking off.  The flight is usually scheduled around a moderately worst-case headwind/(lack of) tailwind.  And so for the 1+00 (in the air) flight, you might be scheduled for 1+30 gate-to-gate.
And if some of the negative factors don't materialize, then you'll under-fly the schedule, which is nice.  Maybe the delay at the gate caused you to miss the "morning rush hour" and you did get to taxi right out, no line or delay, and take off.  There's no precipitation, so no delay for de-icing.  The tailwinds are better than average today, so instead of 1+00, your flight will only be 0+55 in the air.  All good things!
But none of that is really under the pilot's control.
The two places that the pilot can most affect things are, going faster, and getting shortcuts.  Going faster essentially means using more gas, and sometimes guys are willing to do that... the high-school tour group is in danger of missing their connecting flight & being stranded in the hub for the night, let's go fast & get them there!  Another version of going fast is flying at a more "speed efficient" altitude, usually around FL290 or FL300.  If winds are all the same, you'll generally get more speed there because your maximum indicated airspeed (Vmo) and limiting Mach number (Mmo) are very close around that altitude.  The tradeoff is, however, that you are burning more gas by doing this compared to going higher.
If you have the gas to burn, this can typically work.
Also, you can request shortcuts.  Depending on the filed route and what's going on in the airspace, this may get significant savings.  From the West Coast to DFW or IAH, you're typically routed around the north or south side of White Sands.  But, if it's Saturday night and the restricted area is cold (not in use), then you may be cleared direct right through it & save some significant time.  Of course, requesting shortcuts also saves gas (unless it takes you off a wind-optimized route -- rare but possible), so there's no real reason not to do it on every leg.
ATC may or may not cooperate with your plans.  If the restricted area is hot, then you don't get the shortcut through it.  If you're inbound to a busy terminal area (DFW, LAX, IAH, BOS, etc) then ATC probably has a sequence in mind, and they won't approve anything that changes the orderly flow of aircraft into the arrival.  In fact, they may assign you a speed in order to fit the sequence together.
Other than that sort of planning, though, they typically don't mind if you fly fast, and if they aren't too busy, ATC usually approves requests for shortcuts that don't have you driving through restricted areas (or other special use airspace).
How much time can you make up as a pilot?  If you really want to burn the gas, you might make up 5-10 minutes by going fast on a typical 1-2 hour flight, but those extra minutes are getting pretty expensive when you do that.  Shortcuts may give you another 5 minutes or so, in the best case.  (Longer flights tend to be more direct, as a % of the time, so you can't get the bigger & bigger time savings on the longer flights with shortcuts as you do with speed, compared to the short flights.)
But when a pilot tells you that he's going to make up 20 minutes off the planned flying time, most of that will probably be already baked in (tailwinds, no delays, etc) rather than things that he's doing differently than he otherwise would.  (It's still a nice line on the PA, though.)
And some days, none of the above works the way you hope, and the late flight doesn't get any earlier, or even gets later, despite your best efforts.  Speed, time, and distance can just be a bear, sometimes!

"Block" times are most often padded to cover any delays like this. FlightStats has a good explanation of what goes into calculating block times.  The short version is that carriers publish the "quoted" time it takes to go from block-to-block.  Pushing back from the departure gate to pulling into the destination gate.  As shown in the FlightStats link, some quote a shorter duration for the same segment.
On the destination side, nobody ever complains that their flight landed early. Problems for the airlines that do this is that when a plane is on the ground, you're paying money to the port instead of making money flying the plane.
Note that not all airlines have the same trip duration listed for a given flight segment. This can be tough to determine because such overlap generally requires one end be a large hub, and on the East coast US, these large airports are often slot controlled.
Padding block times helps accommodate WX (Weather), headwinds, tailwinds, etc. All at the expense of $$$.

Further Reading:
Interesting info on actual performance vs. Airlines published block times:  http://projects.fivethirtyeight.com/flights/
Also background on how that infographic is built and what factors into the decisions: http://fivethirtyeight.com/features/how-we-found-the-fastest-flights/

"On the destination side, nobody ever complains that their flight landed early." Hmmm .... I don't enjoy kicking my heels near the door of a deserted small airport late at night, just because the flight landed 15 minutes early, there was no queue for baggage, but the car that's coming to pick me up doesn't know about that (and I have no way to contact it). On the other hand if the flight is late, the car driver is getting paid by the hour to wait for me!

Sounds like a great argument in opposition to padding block times!

"Problems for the airlines that do this is that when a plane is on the ground, you're paying money to the port instead of making money flying the plane." Not necessarily. In my experience, at least, they just reduce the time the plane is scheduled for the layover by roughly the same amount, so the actual time spent on the ground (if everything's on time) ends up about the same. I've seen flight schedules where the plane's next flight was scheduled to depart something like 15 minutes after the scheduled arrival time, even on 737-size aircraft.

I would argue that this is a gamble, and an exception rather than the rule.  A carrier can take this approach, but if it backfires there is a high likelihood that stats for TWO flights will go bad instead of just one (late arrival dominoes into late departure).  How a given airline plans ground operations can vary by city, etc. as well.  If an airport is a Maintenance location for Carrier X, they would more likely plan more time on the ground to perform tasks.  This is opposed to a city with maybe 2-3 flights per day for Carrier X, where in-depth inspections are less likely.

Man this got way off-topic! :)

A currently valid illustration of this idea is here:  https://www.google.com/flights/#search;f=SEA;t=LAX;d=2016-05-20;r=2016-05-24;tt=o;so=d   | This probably won't work after May 20th, 2016.

On NMOC (Network Manager Operations Centre) there is one member of each airline, and in case of fleet delays, due to weather for example, they discuss and instruct the ATC  to expedite one or some flights, clearing them to fly direct, and sometimes, overtake leading traffics on the queue.

Are you saying there is a group of airline representatives that instructs ATC which flights to expedite? What part of the world is this?

These group of representatives are part of the ATC management flow control, and they, together, decide how to decrease the delays, expediting who really needs, in order to avoid further delays, impacting the ATS. Your comment seemed to me kind of prejudice, however, the team work really work.

I did not mean to be critical, I'm just curious about the process. Is this more of a day to day thing, general process improvement, or both?

CFMU is the standard name of the Unit. It works 24 hour a day, and mainly coordenates with the RTCC and TWR Controls, minimizing the delays, caused by weather and some other disruptions.

@eduardoguilherme: you should edit the question if the clarifications are correct (I did it this time; revert or fix if you don't think it's correct)

@fooot, the network manager approves flight plans and assigns departure times for them in order to avoid congestion both at airports and in sectors. When there is a disruption (and there are always some), they coordinate with airline dispatchers which flights can accept some delay and which should get priority because they would cause further disruption somewhere else. It is the network manager that eventually assigns the slots, so they ensure (or at least should) all operators get equal treatment.

@JanHudec thanks, that helps, I understand better now.

I am not a ATP, but I would be surprised if commercial flights went faster to make up time, even if they were delayed. The reason for this is that it is much more expensive because you burn fuel faster. To go at top speeds it is not a linear relationship and you could spend a lot of money to get a marginally faster time of arrival.
One free way to increase speed is to take advantage of winds at altitude. So, for example, if there are known to be favorable winds at 40,000 feet, you increase altitude to that level.
You do not need "permission" to go faster. The pilots are the bosses and ATC are the servants, not the other way around. If a pilot wants to go faster, he goes faster, and notifies ATC of the change and they adjust what they have to.

Airlines typically will add more fuel and increase the cruising speed to try and reduce the amount of passengers who will miss their connecting flights. Mis-connect costs can add up very quickly and spending more on fuel can be cost effective in cases like that.

@MikeSowsun Ok, I guess it is a judgement call. The ATPs I talk to always seem to be complaining how the airline wants to cut their nuts off for using too much fuel.

It is true that airlines always want to save on fuel costs. But in some cases, a little extra fuel cost could save the cost of overnight hotels and meals for 20 or more people. Cutting 30mins on a 10 hour flight just might make all the difference.

On some planes (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster.    Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.
Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction,  therefore often a flight can go faster than the planners assumed.

Are you saying Airbus planes have a "sprint mode"? I can't find anything about that. There is an adjustable cost index on modern aircraft which trades fuel vs. time.

authors: Пламен Ангелов


text:
Can a sonic boom produced at 60,000' be heard on the ground?
The Concorde normally cruised at an altitude of 55-60,000 feet, but wasn't allowed to fly over populated areas due to the noise it produces. Can the sonic boom of an aircraft at 60,000 feet be heard on the ground?

Civil supersonic flights are not allowed over US land, due to possible sonic boom effects on the ground. Actually this is a long and more complex story.

Yes, a sonic boom produced at 60,000' can be heard on the ground.
First of all, a sonic boom consist in a steep increase of air pressure, followed by a slow, linear decrease below the nominal ambient pressure, and again a steep increase back to the nominal pressure. It is therefore called N-shaped wave or just N-wave. Here is a graph with several sonic booms, measures by NASA and found on Wikipedia:

The same wiki page cites a document from NASA
Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      80,000 (24,000)  0.9  (43)
Concorde SST    2      52,000 (16,000)  1.94 (93)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    60,000 (18,000)  1.25 (60)

These measurements are from aircraft with different altitude. As sound pressure depends from distance like  $p\sim\frac{1}{r}$, one may calculate the pressure for a certain altitude as in the following table. However, this assumes that the aircraft causes the same "boom intensity" at that altitude, which you should doubt at least for the SR-71.
Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      48,000 (15,000)  1.44 (69)
Concorde SST    2      48,000 (15,000)  2.07 (99)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    48,000 (15,000)  1.5  (72)

As you can see, the Concorde is the loudest aircraft, the most comparable F-104 (speed, altitude) produces just 40% of its sound pressure. But the F-104 is also much much smaller than the Concorde.
The Space Shuttle is very loud for its low speed. However, it looks more like a flying brick than an elegant, streamlined aircraft, so no wonder that it creates strong shock waves.
The SR71 seems to be very quiet for its speed, but as said, I don't think you can pull it down to 48000ft and expect the same behaviour. However, a sonic boom starts to disperse in some (larger) distance, may be this already happened for the SR-71. (Also, it's a spy plane with a very special shape - may be, this reduces the boom, too).

It has to be said that it is hard to translate the numbers into a comparable sound level, because what makes up the loudness is not only the maximum pressure, but also the rise time.
As counter-example, the air pressure changes by 130Pa every meter of altitude (at ground), and you don't hear the change of pressure when standing up from your chair (~100kPa)
Also, a sudden noise appears to be much louder than a noise slowly increasing to the same level - and the bang has the most sudden wave form possible. (Listen loud music with earphones - when the player clips a second, the first moment after really hurts)
However, there is a long table on Wikipedia listing noise sources and their levels. For example:
Trumpet at 0.5m:                63Pa
Jack hammer at 1m:               2Pa  (I'd say: a little quite...)
Loudest human voice at 1 inch: 110Pa

These levels are effective sound pressure. To translate a perfect N-wave with given maximum pressure to effective pressure, you have to multiply the value by $\frac{1}{\sqrt{3}}\approx0.577$.
Thus, the sonic boom of the Concorde has an effective value of 57Pa, which is comparable to the trumpet in 0.5m distance.
(As said, there is still a difference, because the boom is a sharp, short noise, but it gives an idea.)

By the way, I just stumbled on another document, about primary and secondary sonic booms.

It states that you hear a primary sonic boom coming from the aircraft within a lateral distance of ~20nm (solid lines) as well as a secondary boom within a distance of 60-85nm (dashed lines). This secondary waves are a reflection of the upwards travelling shockwaves from the aircraft at the atmosphere.
The secondary boom is not a short, loud bang, but a longer and less intense rumbling, making it difficult to identify the source.

Perhaps worth adding a simpler-language note that states something along the lines of "You can see, therefore, that an aircraft at higher altitude does produce a quieter boom than one at lower altitude, which is due to the lower air pressure, but that there will always still be a sonic boom if the aircraft is flying within the atmosphere" - the data etc you provide does show this, but I think it's perhaps worth spelling out as a summary and to more directly answer the question.

For a second there I thought I was reading physics.se

Hehe, your comment about the Space Shuttle looking like a "flying brick" made me smile. Thanks! :-)

60000 ft is only ~11 miles. That high up the sound actually travels over much larger an area. The space shuttle re-entered the atmosphere much higher than that and you could hear the booms from it very well when it would fly over.


text:
Are grass strips more dangerous than tarmac?
There are a couple of flight schools near me. One is at a large airport, they use Piper Tomahawks primarily to teach. Naturally, they use well maintained, tarmac runways to takeoff and land. This school has had no accidents in the last few years and no fatal accidents for much longer than that.
The other school often use grass strips in fields and use Ikarus C42s and Cirrus SR22T models. This school has had 3 accidents in the past 2 years, one of which involved a fatality and all of which wrote off the air-frames.
I'm pretty sure this isn't due to the type of aircraft (as globally, they all have similar safety records) nor the instructors (both schools use very experienced instructors).
So are grass strips more dangerous to use as a runway and if so, why?

I think focussing on type of runway alone is not enough. You need to look at all of the operation. And first and foremost, what were the accident causes? Are they related? Was it „just bad luck“? And so on. No answer possible without more facts, I believe.

Correlation does not imply causation!

@J.Hougaard That is unhelpful. This is why the question asks if my assumption is even true.

Why down vote? If the premise is wrong, that can be explained  and/or edited.

Were the accidents all landing or takeoff accidents? What were the details?

@GdD Takeoff every-time. Unfortunately that's all I know.

"Tarmac" tends to be used in Europe/ UK to refer to a specific type of paving material (Tarmacadam) which does not apply to all hard-surfaced runways.  In the US in the airport context, "tarmac" is often used to describe a "ramp" area regardless of construction, but would not generally be applied to all hard-surfaced runways, e.g. concrete runways.  The question could be improved by avoiding the use of the word "tarmac".

Was something removed from the question?

@quietflyer In the UK, "the tarmac" (with "the") also refers to the paved areas of the airport and especially the ramps, regardles of what they're actually paved with, whereas "tarmac" (on its own) refers to what is technically called asphalt concrete, i.e., the surfacing material made from gravel bound with asphalt.

@copper.hat Click the "edited x hours ago" link below the tags to see the edit history.

Glad we got the "tarmac" story in.  "Macadam" is named after Sottish engineer John McAdam, who standardized the size of the gravel used in road construction.  This gravel, mixed with higher melting petroleum "tar", is the real "tarmac".

One might ask whether actual takeoffs and landings are really all that dangerous, regardless of surface?  From what I've seen (admitted a limited subset) it seems the problems have more to do with things like overloading, density altitude, engine failures on takeoff, and so on, rather than the actual strip itself.

Edit was entirely over-zealous and not necessary to begin with.  Questions can speculate, that's what they do.

Cloud, you are making a huge inference from a few small data points.  But in any case, to the basic question, which is actually a very good one:
In terms of the chance of getting killed, (what you seem to be looking for), maybe, marginally, but not enough to rule out operating from grass.  If you know what you are doing, and make allowances, I would say zero.  In terms of non-fatal incidents, maybe a bit higher, depending.
On the plus side: A grass surface is more compliant than a paved one because the tires have less traction.  Grass is much easier to handle flying taildraggers because there is some lateral give with respect to tire side loading.  A tailwheel airplane on pavement is much more skittish and easier to ground loop.  This is also true of tri-gears but much less so because they are already naturally stable while rolling. In both cases however, most people will find it easier to maintain directional control while on grass because of the traction compliance.
On the down side: Somewhat less braking dry, quite a bit less braking wet (wet grass is quite slippery, as anyone who tries to run on it without spiked shoes quickly discovers).  Rolling resistance is higher so take-off distance can be longer than published numbers, which are based on a dry paved runway, and in marginal conditions this has to be accounted for and this varies with how long the grass is at the time.
Bottom line: If I'm in a taildragger I'll much prefer a grass runway. In a tricycle airplane I'll prefer a paved one.  Overall I would expect to see more runway excursion incidents on grass, like landings in rain or in morning dew where pilots slide off into a fence when they discover, surprise surprise, they can't stop, that kind of thing.
That being said, I would never say that a grass runway surface is inherently more dangerous IF the pilot is properly trained in what to expect (especially landing on wet) and makes allowances for it.  The only kind of fatality I would directly attribute to grass would be a takeoff fatality where the airplane's take-off run was extended and it struggled into the air at the far end and stalled out.
In the end though, regardless of this factor or that factor, these things really come down to that old standby, BAD AIRMANSHIP.
More than boating, aviation is fraught with hidden hazards waiting to trip you up.  But if you are educated and trained, they are neutralized and can't get you unless you let your guard down.  You have to approach things in flying this way, or you will worry yourself out of the activity before you ever really get to enjoy it.  On the other hand, you are asking the right kind of questions so this is good.

To an extent, then, the answer is a qualified "yes". New pilots may not yet have the skills to handle the subtleties of a grass strip and that may have led to the additional accidents noted in the OP's premise; however, an experienced pilot who understands the differences will know what to expect and accommodate the differences.

Well, OK, that's the answer to the question in the question, not the question in the title.

you will worry yourself out of the activity before you ever really get to enjoy it ... it's funny you say that I have thought about not continuing with the pursuit more and more, the more I read about these kind of incidents and how regular they are, but then again I think it's useful to read these things so you are better prepared as a beginner... thanks for the informative answer either way.

@Cloud that's an impression I've gained from a lot of your previous questions, which could sometimes reveal what comes across as an over-obsession with risk.  To the extent that your approach to all this is becoming more practical, that's great.  Your question was an excellent one.  You framed it in a way that some ppl weren't happy with, and which made me think you were over-analysing risk, but it looks like you are on the right track.   If you are being taken to grass strips during your training, you should ALREADY be getting this kind of information from your instructor.

@Cloud The answer to all these type of questions that you ask is: it depends, you know already that it will depend on many factors, but that doesn't stop the next question coming along.  You are trying to rationalise risk out of flying in a way that is not reasonabe.

@Cloud Want to know a fun fact? Flying is a LOT more dangerous than not flying. Seriously! It's at least 99438413294821 times more dangerous. If you're risk averse, you might want to choose not to do it...

I'm surprised that braking would be worse on dry grass than on pavement; one would think that the increased drag from having to wallow through the grass would improve one's stopping action.

Lol nobody lands on grass THAT deep... although I think you really mean regular grass cut to say 2 or 3 inches.  The grass blades being rolled flat by the wheel don't provide that much friction, even dry, so you notice the difference between it and asphalt.  But unless you're doing a special STOL landing into a very small space, braking shouldn't be a big deal and if you really need brakes it's usually because you landed long and hot.  The pilot landing at a breakfast fly-in early, so there is still dew, and who is a little fast and long, is the one who ends up in a fence at the far end.

John K already gave a great answer about the runway surface itself and there are some other points that might be worth mentioning too. Grass runways are often uncontrolled, short, rough, obstructed, and generally different from paved ones. That's a big generalization, of course, but it's worth thinking about the wider runway environment.

Uncontrolled. Whether or not uncontrolled airports are more 'dangerous' than controlled ones is very debatable although a tower does provide some level of information and direction that doesn't exist at uncontrolled airports. Obviously, this applies to any uncontrolled runway, not just grass ones, but a pilot who isn't comfortable with an uncontrolled environment might theoretically be at higher risk than one who is, if only because of issues with situational awareness or radio work.
Short/rough. Some grass runways are almost as smooth as pavement (Triple Tree, for example). Others are very rough and back country grass strips may not be maintained much, if at all. At least in the US, private pilots are trained in short- and soft-field landings and takeoffs but any piloting skill can degrade over time. As well as actual flying skills, pilots who only fly from long, paved runways might get complacent about performance calculations, which can make all the difference in some cases. Even taxiing can be challenging if the ground is rough and a pre-landing inspection may be useful. Or even a pre-takeoff inspection!
Obstructed. Especially at private or back country strips, the runway may be close to trees or other obstructions. That requires the pilot to be comfortable with short-field landings in particular.
Different. A grass runway can attract deer or other animals. You might have to do a low pass to move them off the runway before landing.

Having said all that, private pilots are trained for all of those situations and there's nothing 'dangerous' as such about landing on grass and it's not a big deal at all. Many pilots consider it more fun, especially in a tail-wheel aircraft. I couldn't find any statistics about grass vs paved surfaces, but there are many factors to consider and in general a pilot's personal experience and comfort level will count for much more than the runway surface. As with any new scenario in flying, if you aren't comfortable then find an instructor and go and try it out before you do it solo.

Though deer (and other critters) are quite happy to hide in the brush alongside infrequently-used paved runways, and run across the runway when they hear your plane coming.  Also, the question could be extended to dirt runways, since there are a lot of places out here in the west where grass doesn't grow.

I want to add one more thing that neither existing answer discusses, but which I feel is relevant here.
Grass strips are more difficult than hardened ones to spot from the air, especially if you're not used to them and know exactly what to look for.
This doesn't make them more dangerous per se (as a pilot, you should only continue the landing if doing so is safe, which includes remaining on the proper glidepath toward your intended landing point and not drifting laterally), but my experience is that it's much easier to midjudge your glidepath, or the distance to the threshold, when the runway doesn't stand out clearly from the surroundings.
It's a trap I fell into the first time I tried to land at a field with only a grass strip, being used to a field that has both a paved runway as well as adjacent grass strips (both of which I'd both taken off from and landed on). I lost the strip I was aiming for, as I recall during a traffic pattern turn, and we (instructor and I) ended up going around for another attempt.
A paved runway is plainly visible from well away, and hard to mistake for much else: it looks like a straight stretch of wide, gray road that appears out of nowhere and doesn't go anywhere, clearly cut out from the surroundings almost no matter what the conditions on the ground are. A grass strip, on the other hand, can easily look like nothing more than a slightly different shade of green compared to the surroundings, hopefully with something to mark the thresholds and edges. To confidently recognize that for what it is, from a distance, takes more practice.


text:
What technologies exist to find an aircraft position after it crashed out of line of sight?
What is the best way in the manner of products to find an aircraft after it crashed out of line of sight. Are there defined standards, and what are the selection criteria?

How big of a UAV? If they are large enough, an FAA registration number is required to be visible on the outside.

Since you should not be flying it out of line of sight it should not be crashing anywhere you cant watch it crash...

Can you tell a bit more about tge type of aircraft and type of mission you are flying? It seems to me that first of all, you don't want your 200 pounds drone to crash as it is a safety hazard to those on the ground. I would recommend constant telemetry between the drone and a operating station so that the location can be tracked. How you achieve that depends on the drone, its mission and the environment.

The drone could well be within the operator's line of sight, right up until the point that the craft falls to earth.  The requirement is line-of-sight to the drone, not to the ground under it.  That all said, opinions & product recommendations are entirely off-topic here. VTC

It depends on the UAV.  Many consumer UAVs eg DJI, etc. track the position of the drone via GPS and log it so you can find the crash site quickly.  Others emit beeping noises so you can locate it by sound.

Thanks. What about crash position inducator cpi systems, i havent seen any uav mounted with these system just for helicopter. And following voice signal may be difficult to hear. What is your opinion about cpi?

Any recent Android mobile phone has "find my device" feature now, even if no additional apps are installed.
Attach an Android phone with the dedicated Google account logged into to the AC and you will be able to find the location, say, by visiting Google website from your tablet. You can buy a ruggedized phone that is more likely to survive the crash.

Good idead, how to handle battery problem guess will operate 10k hours and where will i mount it to guarante it will survive after crashed and signals not blocked?

@K.Ense "operate 10k hours" Find me a battery source that is light enough to put in a phone and fly it around on a consumer drone and will operate anything (beyond a simple digital wrist watch, not a smart watch) for 10k hours & I'll pay you good money for it!

@FreeMan here i want to say that i dont want to charge it before every flight so only way is continusly connect battery to supply and we can use 10k hours?

@K.Ense 10,000 hours is 416.6 days. Do you know of any rechargeable battery powered device that will last that long in continuous use? Especially something as power hungry as a smart phone? Also "guarantee it will survive after a crash" - I've seen people drop cell phones 1 meter from their pocket and break the screen. I think that guarantee is highly unlikely in a flyable package.


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Is the September 11th the only time a plane was crashed into skyscrapers?
I wonder if there has been other plane crashes with skyscrapers in history, except the one of the World Trade Center.

It was attempted in 1994 https://en.wikipedia.org/wiki/Federal_Express_Flight_705

There were threats to intentionally crash into a nuclear reactor in 1972 on Southern Airways flight 49.  https://en.wikipedia.org/wiki/Southern_Airways_Flight_49

Intentionally with a large aircraft, yes. There was however an instance in 1945, where a B-25 Mitchell collided with the Empire State building. This however was an accident.
There have been several suicides by airplane where the aircraft was deliberately crashed into buildings, such as the C172 which was crashed into a Tampa FL high rise in 2002 or the Piper Dakota crash in Austin, TX.  There was also a case of an accidental crash of an SR-20 into a NY high rise apartment building in 2007, killing baseball player Cory Lidle.

Here's another intentional one:. https://en.m.wikipedia.org/wiki/2002_Tampa_Cessna_172_crash

One more: https://en.m.wikipedia.org/wiki/2010_Austin_suicide_attack

Cory Lidle accidentally flew his SR-20 into the side of a high rise in NYC in 2006.

All excellent examples.


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Can ATC terminate flight following AND approve (arbitrary) frequency change while still inside Class C airspace?
Unusual (for me) event inside Class C. Can ATC terminate flight following inside Class C and approve frequency change.
Background: Requested and received VFR FF at 6500 msl prior to approaching ONT Class C (top is at 5000). Intent was to over-fly ONT and not enter Class C, however after reaching north of the field, ATC said “free to descend altitude at your descretion ” (Point A). My response, “6500 ft decending to 4500”. At about point B, I dropped into Class C and continued to 4500. After leveling off, still in Class C, ATC said “Squawk VFR, frequency change approved.” I responded “Squawking VFR, and immediately departing Class C to the North”. (Point C) His response, “You don’t have to do that as the tower still has you on radar.” I said “departing Class C to the north”
Here is my confusion: First squawking VFR is not an issue, I’ll squawk whatever is requested and maintain my own flight separation but when he said “frequency change approved” I would no longer  be in radio contact in Class C if I actually did as approved. This would mean, to me, I am illegally in their airspace.  What am I missing???

Jim S asks an interesting question.  Can ATC ask you to do something which is contrary to the regulations?  The answer is they can, and just because they do, does not change the regulations.
The practice of advising aircraft to switch to advisory frequency and squawk VFR is common here, in Class C airspace, and I have experienced it in Class B airspace as well.
Discussing this with the ATC supervisor once, it was explained to me this way: The controller knows where you are going, knows your intent, and believes that he can manage the traffic in the area effectively if you leave the  frequency. So for the controller it is an issue of risk and workload management.
With students, this creates a good learning opportunity to have them "monitor" one radio, while using another.  No official guidance on this, but it is common practice. So if you are not familiar with this, have an experienced pilot or CFI demo it to you.
Keep in mind that this is the same process for IFR aircraft making approaches to non-towered airports.
Arguably, ATC can authorize deviations from 91.130, as @DaveCFII points out. Certainly that covers temporary frequency changes to check WX and things like that, but it could be interpreted to have broader scope is that it could be used to terminate communications near to the point where an aircraft leaves Class C.
Having said this, I would prefer that ATC state something like, "communications deviation approved."  Of course that will not happen on a busy frequency.
Having said all this, it is important to remember that the pilot has final authority over a flight, and the FAA in the Granby LOI makes it clear that ATC does not have the requirement to point out to pilots what regulations apply to their operation.  So a pilot who is uncomfortable with this procedure, might monitor ATC on one radio, and broadcast their intents on the advisory frequency. This way they can fully comply with the regulations. Most aircraft have dual COM radios.  If not, delay your frequency change until you are clear of Class C, to remain in strict compliance.
Ref: Granby LOI  https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/data/interps/2006/granby%20-%20(2006)%20legal%20interpretation.pdf

Thank you for the detailed discussion. This was my first experience of being “cleared” for something “questionable”. You said, “The controller knows where you are going, knows your intent, and believes that he can manage the traffic in the area effectively if you leave the frequency. So for the controller it is an issue of risk and workload management.” I believe that sums it well.

FYI - PPL/IFR 500+ hrs w/about half w/CFI/dual. One would think that I would have been taught or experienced this before. Note to CFIs: teach this anomaly (perhaps you already do). Thank you for your discussion.

FWIW, CFIs should be teaching students how to monitor a second frequency for things like picking up ATIS/ASOS while still talking to ATC/CTAF.

I agree StephenS, but in this case it was a singlle radio without monitoring capability. Although, still possible by getting permission to temporarily leaving the frequency. Probably doesn’t apply here.

@JimS, if you asked for a temporary frequency change, and then you were outside Class C, then that would be similar to the controller switching you when you were close. This is an example, of when judgment comes into play, and you decide whether you really break the rules, or you stick to the strict interpretation of the rules. One could always ask the FAA for a LOI on this topic, however, think carefully about that, because the FAA tends to stand by their previous LOIs in enforcement actions. It might be better for someone if the matter was not formalized.

@StephenS, et al., I teach all my primary students operations maximizing their use of single and dual radio circumstances. It is an essential skill, even if one spends most of their time in the backcountry.

@mongo. I believe the “strict” interpretation is clear (maintain radio contact) and the “loose” interpretation appears to be, “I am not going to talk to you again, free to go”.  I don’t think I want to see an LOI written for this. It appears to be far more common than I thought.

The requirement to maintain two-way radio communications is FAR 91.130(c). But regulations have to be read as parts of a whole. Read 91.130(a), which says:

Unless otherwise authorized by ATC, each aircraft operation in Class C airspace must be conducted in compliance with this section...

"Frequency Change Approved" is ATC authorization to deviate from the requirements of 91.130(c).

I think you're right, and it looks like this is an important point that all of the other answers have missed: ATC can authorize you to deviate from 91.130(c), in which case deviating from 91.130(c) is completely legal. I didn't know that until I read this answer. I had posted an answer previously, and my answer said that you're still required to obey 91.130(c) even if ATC says that you don't need to. It looks like that was incorrect, so I've deleted my answer.

Were you perhaps inbound to CCB?
If so, I agree with the comment by @StephenS:  That once you are cleared all the way out of the airspace, ATC will release you by effectively saying, "I'm not going to have anything more to tell you, you don't really need to stay on frequency anymore" (even if this might be a technical violation under 91.130.)
Because ATC expects you to go to the CTAF frequency, they know where to find you.  They may well be monitoring that frequency, and can broadcast on it if needed.
If you have dual radios, and want to be extra safe, keep ATC on Radio #1, and start your CTAF calls on Radio #2.  Double-check your mic-setting with each transmission, so you know which frequency you're transmitting on. You can still hear ATC if they try to reach you even after approving a change.

Your speculation is correct. ATC was informed that KCCB was the destination and that my course was to the common visual point of entry (San Antonio Dam). I only have one radio (but he wouldn’t know that) so I now believe he expected no further issues with me and had other things to do..... I do believe it was correct to remain on frequency until clear of C (one radio).

If ATC tells me "no traffic observed, frequency change approved", he's saying he has no reason to call me again. If I had one radio, I'd switch to CTAF then and make my first call. Might be a violation, but IMHO that seems a smaller concern than hitting another plane due to not making CTAF calls early enough.


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Can I do a CAT III ILS approach if minimums are above CAT I?
I was going to an airport with weather at minimum for CAT I approach. Not wanting to know whether or not I could make it I thought about asking ATC if I could do a CAT III approach even though the weather was still above minimum for CAT I. Eventually the weather got better but my question is: Could I have requested from ATC and be granted a clearance for a CAT III approach (abiding by the CAT III weather mins) even thought the current weather was above CAT I minimums?

In order for ATC to clear you for an (operational, not practice) Cat III approach, the airfield would have to operate under Cat III Low Visibility Procedures (see https://www.skybrary.aero/index.php/Low_Visibility_Procedures_(LVP)). As these are normally very restrictive in terms of permitted movements on the airfield and especially around runway areas, I would expect airport operators to only invoke LVPs to the level that is operationally required. Therefore I would assume that the answer would probably have been “no”.

Possible duplicate of How do you choose CAT II vs. CATIII ILS?

Not a duplicate at all. This question is, CAN I fly the Cat III; the other question is "when might one choose to fly ..." one approach or the other.

My airlines is very specific about this. If the weather is below CAT I, always do CAT III (assuming all requirements are met)

Yes, you can request it. We (ATC) may or may not grant it. It can be quite complicated for us to establish CAT II/III procedures, including having to switch over to backup power, turning on stopbars and other protective measures, limiting aircraft and vehicle movements on the maneuvering area, closing certain taxiways etc.
Doing a CAT III approach is not just looking at a different chart, it can involve a lot of complicated procedures for the airport!

Switch to backup power ?

If the weather is marginal like OP is describing, would ATC usually be prepared to switch to CAT II/III if requested?

@cavver Where I work we will switch to diesel generators during LVP because they are more reliable than external power. The system will then fall back to external power if a diesel generator fails (switch over time less that 1 second during LVP)

@TomMcW Yes, of course.

J.Hougaard .. thank you for your valuable answer.

I assume that the airport has a published CATIII approach chart , i.e. the ILS system is CATIII ready .
You should request a protected ILS .approach from the ATC. See what happens when doing an autoland without requesting it to be protected


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Are there any airliners capable of vertical climb with engine thrust only by pointing the nose up?
So, sort of inspired by this question, I was wondering if there were any passenger airliners with enough thrust to fly straight up, supported purely through the thrust of their engines rather than the aerodynamic lift generated by their wings - so that once it's flying along, it can just point its nose at the sky and go straight up; if you think about the launch of the Space Shuttle, you’ve got the right general idea. According to some of my comments, this is apparently called a "zoom climb". Note that I'm not asking about VTOL, since some aircraft that are capable of this may not be capable of VTOL due to a lack of thrust vectoring.
I know that some military fighter aircraft are capable of this, but based on some research with Wikipedia, it appears that the Boeing 747, Boeing 787, and the Airbus A380 can't - though the 787 would almost be able to do it if it had four engines rather than two.
Are there any passenger aircraft that are capable of doing this? Obviously they wouldn't do so while passengers were on board, but I'm just interested in the ratio between Operating Empty Weight and Maximum Thrust.

Jets are kind of hopeless. The maximum thrust is like half of minimum weight. Props are close at low speed. Maybe Tupolev Tu-114 has some potential as its the most powerful prop plane.

@user3528438 According to the formula for propeller planes on the Wikipedia page for thrust-to-weight ratios, the values vary dramatically based on how fast it's going; at its maximum airspeed, it's nowhere close (about a ratio of about .19), but it goes up the slower the plane goes.

@ymb1 I just realized I removed your edit, just to explain: I think the question is basically about thrust to weight. Zoom climb is about converting horizontal speed to vertical speed, which (of course ) heavily involves aerodynamics. Question seems to exclude aerodynamics. I bet most airliners are capable of brief zoom climbs...

@ymb1 My question isn’t about VTOL because a plane that might not be capable of VTOL but still qualify for my question if it’s not capable of vectored thrust. If its thrust is horizontal, then it would need to take off horizontally before pulling back and pointing its nose at the sky to climb vertically.

@ymb1 Is it better now?

I apologize my misfortuned edit of removing the "zoom climb", now this question is however, a mix of zoom climb and VTOL. In a zoom climb a plane is not supported by engine thrust alone, the engine thrust prolongs the zoom climb, and you gather the speed to make the zoom climb with engines, but by definition zoom climb is an event where horizontal speed is converted into vertical speed. This is done with the help of the magic that is aerodynamics :)

If you want to know about zoom climb and passenger planes, your question might be something like Are there airliners capable of zoom climb and Do any airliners have enough engine power and structural strength to execut a zoom climb, even briefly.

Just for reference, here is a link from-world defense.com link,
showing fighter jets. you can see the thurst to weight ratio, and also the actual thrust and weight of each aircraft. from here you can understand that they are very overpowered, and even capable to accelerate vertically.
And, they have very short wings meaning they do not use lift as an airliner- with long wings which is suitable with lot's of lift.

No, there are few planes that can do this at all. In order to be able to climb out straight up you need a thrust-to-weight ratio greater than 1. In other words you need enough thrust to propel the full weight of the aircraft up without the wings generating lift.
Wiki provides a brief list of aircraft and associated thrust to weight ratios, the Concorde comes in on top at 0.372 with full afterburner but this is at max weight. Although at its empty weight it was pushing a 0.877 ratio. Even running on fumes would not have done it at full afterburner in the Concorde. For comparison the 757-33 has a ratio of 0.6 at Operational Empty Weight assuming a maximum thrust of 42,600 lbf per engine.

Wayne Handley had the Oracle Turbo Raven which at the time at least was the only such aircraft with such a thrust-to-wait ratio:  https://www.youtube.com/watch?v=DvxqbX3s_oE

The Turbo-Raven was a single seat-aerobatic craft with not a single passenger, it was not an airliner.

@GuyInchbald of course, which is why it was a comment.  I just thought it was an example that might be of interest to others.

Then may I suggest you modify the assertion that it was the only "such" aircraft (which in the present context implies it was an airliner) to, say, the only civil aircraft?

@GuyInchbald I see your point.  I can't edit my comment at this point, but if I could I would have rephrased to "was the only aircraft with such a thrust-to-weight ratio".


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What is the purpose of having different ILS categories?
What is the difference between CAT I, II and III ILS approaches? I understand that the different categories are used in different weather, but what are the differences, exactly? Do flight crews have to act differently when flying a CAT III approach as opposed to, say, a CAT I approach?

Possible duplicate of What are the lowest authorized minimums for each ILS category?

@RalphJ Not a duplicate as such. This question is about why different categories exist. The other question is specifically about what the different minimas are. The answer to this question could also include details about crew authorisation, equipment (airborne and ground based) and differences in ATC procedures for different approach categories. I will write up an answer later today if the question remains open.

The different categories of ILS's and instrument approaches in general give different types of precision for various types of conditions (not just weather).

Instrument landing system - ILS - is a very common precision approach system used in airports around the world. An ILS consists of two ground antennas and an airborne received in the aircraft. One of the ground antennas, known as a localiser, transmits a narrow beam along the runway, giving lateral guidance to aircraft approaching the runway. The other antenna, the glide slope, transmits a vertical beam at a specified angle, giving vertical guidance for aircraft approaching. Together, the localiser and glide slope provides aircraft with an exact path to follow toward the runway.

A localiser antenna
The main advantage of ILS is that is allows approaches and landings in poor weather conditions. Pilots do not have to visually see the runway until moments before touchdown, because the ILS can guide the plane down very precisely. However, there are different standards of ILS. These are named CAT I, CAT II and CAT III (CAT III has three additional substandards: CAT IIIa, CAT IIIb and CAT IIIc).
In order to fly a CAT I approach, the cloud based (ceiling) must be no lower than 200 feet and the visibility must be no lower than 550 metres. This is because the pilots must be able to visually identify the runway no later than 200 feet above the ground to be able to land.
For a CAT II approach, the ceiling must not be lower than 100 ft and the visibility not less than 350 metres.
CAT IIIa has a minimum ceiling of 50 ft and a minimum visibility of 200 metres.
CAT IIIb has no minimum ceiling, but there must be at least 50 metres of visibility.
For a CAT IIIc, which has not actually been implemented anywhere, there are no minimum limits for ceiling and visibility.
As you can see, CAT II or III approaches allow pilots to land is extremely bad weather conditions.
So if CAT III is so great, why don't we use it all the time?
In order to use CAT II/III approaches, a number of conditions have to be met:

The ground based ILS equipment must live up to very strict standards, and be very carefully calibrated. As a result, installing and maintaining CAT II/III ILS equipment at an airport is very expensive, so not all airports have it.
In addition to the ILS antennas, there are also strict requirements for other runway equipment such as lighting.
The aircraft must have special equipment that is certified to perform CAT II/III approaches. Again, cost is a significant factor. Equipping aircraft with such fine tuned equipment is very expensive, and if you mostly fly to areas with good weather, it is probably not worth it.
The pilots must be qualified. A normal pilot license is not enough to fly a CAT II/III approach, you need additional training and qualifications to be allowed to perform such approaches.
Air traffic control low visibility procedures result in reduced airport capacity. Because ILS signals are transmitted from antennas on the ground, there are risks of interfering with the ILS signal, resulting in imprecise guidance. The main issue is when an aircraft moves in front of the antennas, partly blocking the signal for other aircraft on approach. Because of this, airports have strict rules for how close aircraft may get to ILS antennas when CAT II/III approaches are in use. Aircraft on the ground must hold further away from the runway than they normally would, to stay clear of so called ILS sensitive areas.

An example of ILS sensitive/critical areas at an airport

Separate runway holding points used when CAT II/III approaches are carried out
We also need additional space between two aircraft approaching the same runway. This is because the first aircraft, once landed and on the runway, can block parts of the localiser signal for the following aircraft. Because of this, the first aircraft must be clear of the runway by the time the second aircraft joins short final. This means we need extra space between aircraft, resulting in a reduced runway capacity.
As you can see, there are a number of factors limiting the use of CAT II/III approaches, which is why they are only used when the weather is so bad that CAT I approaches cannot be carried out.

In this answer to a related question the ILS markings on the ground are shown. They alert the aircrafts to stay out of that area until ATC gives clearance.

@PerlDuck Indeed. The same markings (although not the associated signs) are shown in the third image of my answer.

Re: The pilots must be qualified. I know this is a separate question but let's say I travel with an airliner like Lufthansa or SAS: can I expect the pilots (at least the PIC) to have such a qualification? I'd assume Yes, of course! but am not sure.

@PerlDuck Most likely yes. You don't need to worry about it though. If the crew is not qualified, the flight will simply be cancelled or diverted.

In addition to CAT II/III equipment, also approach and runway lights and back-up power have some strict requirements.

@Sami Good point, I've added it to the answer

@PerlDuck No, many airline pilots are not legal to fly cat 3. The initial qualification is not the limit, pilots must also maintain currency, meaning they must practice cat 3 on a regular schedule or they loose qualification. The extra simulator time is expensive so it is not used if not needed on the routes flown.

In the USA, at the lowest end of the scale, a private pilot can only carry a passenger if current. Which means that they have practiced 3 landings within the past 90 days with the same type of plane and flight conditions/rules. (day landings for a day flight or night landings for a night flight, [6] instrument approaches for an IFR flight) These landings are not required for solo flight.
To be current more generally a private pilot must also have had a flight review within the last 24 months.


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Are military aircraft required to have black boxes?
In the United States, the FAA requires certain types of aircraft to have a Flight Data Recorder (FDR) and/or Cockpit Voice Recorder (CVR).  I understand these regulations to apply mostly to civil aviation.  Does it apply to military aircraft as well?
Another question researched whether fighters have them or not; my question is whether they are required to, and for military aircraft in general, not just fighters.

The answers to http://aviation.stackexchange.com/questions/12401/how-much-jurisdiction-does-the-faa-have-over-military-aircraft suggest that FAA regulations generally are not binding on the military.

Do you mean "do the FAA regs apply," or would military regulations also count as requiring it?

@cpast both preferably, although i'm thinking the faa would have some sort of exemption codified in the cfr.

Military aircraft need not adhere to FAA regulations. Modern military aircraft with digital controls have black boxes, older ones may not.

No. The FAA has no enforcement ability over the US military.
As far as airworthiness and certification, the Federal Aviation Act, Section 610, specifically states that its provisions only apply to "air commerce" and "civil" aircraft.


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How to calculate the thrust of a piston or turboprop engine?
This spawns from a related question. Propeller-drive engines (piston/turboprops) seem to always list their output in horsepower or kilowatts, which are units of power.
I want to know the engine's thrust instead.
How to calculate this?
I know propeller thrust depends on airspeed. What I want is an equation where we input engine power and airspeed (and maybe other parameters), and output thrust.

Well, in a sense it is easy. Power = thrust · velocity. However, that is power output of the propeller. Between power output of the engine and power output of the propeller is the propeller efficiency and somebody else will have to describe that.

The simplest equation uses an assumed propeller efficiency $\eta_{Prop}$and converts power P into thrust T like $$T = \frac{P}{v}\cdot\eta_{Prop}$$
where $v$ is the plane's airspeed.
The tricky thing is to get $\eta_{Prop}$ right. Use 85% for lightly-loaded$^*$ propellers working at their design point. And make sure you subtract the power offtake from the engine for driving the accessories, so you only use the effective power at the propeller, not the rated engine power.
The equation only works if the propeller is in motion, so airspeed $v$ is not zero. For covering the static case, please see this answer.

$^*$The load on a propeller can be expressed by the ratio of thrust to the propeller disc area, made dimensionless by dividing by the dynamic pressure $\frac{\rho}{2}\cdot v^2$. If $T$ is thrust and $d$ is the diameter, the dimensionless thrust loading coefficient $c_T$ is
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{8}\cdot\rho\cdot v^2}$$
Sometimes this is simplified to
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{4}\cdot v^2}$$
Note that this definition needs the propeller thrust at a specific speed. A different way of expressing the propeller loading, which lends itself to using the easy to measure static thrust, is by dividing thrust by the disc area and the dynamic pressure of the propeller tip at rest, with $n$ as the RPM of the prop:
$$c_T = \frac{T}{\frac{\rho}{2}\cdot\left(\frac{n\cdot\pi\cdot d}{60}\right)^2\cdot\pi\cdot\frac{d^2}{4}}$$
and again a simplified form of this can be found in literature:
$$c_T = \frac{T}{\rho\cdot\left(\frac{n}{60}\right)^2\cdot d^4}$$
Generally, a lightly loaded prop has a big diameter and flies at low to moderate speed. While WW II warbirds are still in the lightly loaded realm, all large turboprops (C-130, P-3) are firmly outside of it.

Thanks but what does lightly-loaded propellers mean exactly? Are you talking about something like wing loading or disk loading for helicopters?